Light-detecting electron multiplier with field emission photoconductive cathode

ABSTRACT

A light detector based on the fact that the field emission from a photoconductive material varies depending on a variation in the intensity of the light to which said photoconductive material is exposed, said detector comprising basically a field emission cathode of a photoconductive semiconductor in the form of a pointed whisker, and an electron collector for collecting the electrons emitted from said cathode, an appropriate accelerating voltage being applied between said cathode and said collector.

0 United States Patent 51 3,646,350

Maeda et al. 1 1 Feb. 29, 1972 [54] LIGHT-DETECTING ELECTRON [56] Reierences Cited MULTIPLIER WITH FIELD EMISSION PHOTOCONDUCTIVE CATHODE UN'TED STATES PATENTS 1,300,127 4/1919 Creighton ..313/217 X [721 W Nishida, 2,692,948 10/1954 Lion 091 13Wn 3,175,083 3/1965 Schumacher. 73 Assignee; Matsushita Electric Industrial Co Ltd" 3,233,l l1 2/1966 Plke ..250/2ll Osaka, Japan 3,370,172 2/1968 Hora ..250/213 X 3,449,582 6/1969 Sackinger ..250/213 [22] Filed: Nov. 4, 1968 Primary Examiner-Walter Stolwein [21] App. 773078 Att0rneyStevens, Davis, Miller & Mosher [30] Foreign Application Priority Data [57] ABSTRACT Nov. 10, 1967 Japan ..42/72728 A light detector based on the fact that the field emission from a photoconductive material varies depending on a variation in [52] US. Cl. ..250/207, 250/211 R, 250/238, the intensity of the light to which said photoconductive 313/94 material is exposed, said detector comprising basically a field [51] Int. Cl .1101] 39/12 emission cathode of a photoconductive semiconductor in the [58] Field of Search ..250/211, 213 T, 83.3 IR, 238, form of a pointed whisker, and an electron collector for collecting the electrons emitted from said cathode, an appropriate accelerating voltage being applied between said cathode and said collector.

1 Claims, 3 Drawing Figures LIGHT-DETECTING ELECTRON MULTIPLIER WITH FIELD EMISSION PI-IOTOCONDUCTIVE CATI'IODE This invention relates to a light detector based on the fact that the field emission from a photoconductive material varies depending on a variation in the intensity of incident light. The light detector of this invention is of a novel construction and belongs to none of the conventional types of light detectors such as the photoelectric elements, thermocouples, thermopiles and various photoconductive semiconductors.

The light detector of this invention is based on the principle that the field emission from a photoconductive semiconductor body in a low temperature is affected by incident light. The above principle is combined with a known technique for increasing the electronic emission such as the channel type secondary electron multiplication to raise the sensitivity of the detection of light.

Objects and features of this invention will be clarified in the following description made in connection with an embodiment of this invention and with reference to the accompanying drawings, in which;

FIG. 1 is a schematic diagram illustrating the structure and operation of a light detector embodying this invention;

FIG. 2a is a circuit diagram for the explanation of the operating principle of the light detector of this invention; and

FIG. 2b is a diagram showing characteristics of the circuit shown in FIG. 2a.

Referring to FIG. 1 which shows the structure of a light detector of this invention to be used in the infrared range, reference numeral 1 indicates a whisker or a field emission cathode with an end pointed by an etching process so that an extremely high-electric field can be produced at the end, said cathode being made of a photoconductive semiconductor which is sensitive to light in the infrared range; a bridge 2 for supporting said field emission cathode, which serves also as a heater for cleaning the point of the cathode before each operation; and feedthrough wires 3 connecting said support bridge 2 to lead wires 31. A stem portion of the envelope is shaped to have a deep recess 4 to be utilized as a Dewar flask for receiving liquid nitrogen 5 which refrigerates the field emission cathode 1 through the feedthrough wires 3 and the support bridge 2. Reference numeral 6 indicates an accelerating electrode placed at the front of the field emission cathode l for guiding the emitted electron beam; an infrared ray 7 projected from the outside to the field emission cathode; a window 8 of quartz or crystalline alkali halide for introducing said infrared ray 7; and a channel-type secondary electron multiplier 9. The electron beam from the field emission cathode l is introduced into the pipelike multiplier 9 through the entrance 91 thereof and the multiplied beam is let out from the exit 92 to be imparted to a collector 10. Thus, an output current flows through the resistor 11 and an output voltage appears at the terminal 12. Numeral 13 indicates the accelerating voltage source; 14 a retarding voltage source for appropriately retarding the accelerated electron beam before it reaches the entrance 91 of the electron multiplier 9; 15 an accelerating voltage source for applying a voltage between the entrance 91 and the exit 92 of the electron multiplier 9; and 16 an accelerating voltage source for directing the electron beam from the electron multiplier 9 to the collector 10.

FIG. 2a is a simplified circuit equivalent to the essential part of this invention, in which V indicates the voltage of the accelerating voltage source and I is the field emission current from the field emission cathode l. The relation between the accelerating voltage and the field emission current under vari ous intensities of the incident light projected onto the field emission cathode is shown in FIG. 2b, in which the abscissa is calibrated by the reciprocal of V instead of V and the curves a, b, c and d correspond to the respective light conditions, the curve a corresponding to the highest intensity of light and the curve d to the lowest.

Therefore, if the voltage V, is set at a value corresponding to the point intermediate between p and q as shown in FIG 2b,

thecurrent will si ificantly vary depending on the intensit of incident light. uch characteristics have been venfi in several photoconductive materials such as ln S and Sb S What we claim is:

1. A light detector comprising a field emission cathode of a photoconductive semiconductor; means for detecting variations in field emissions due to changes in light; a channel-type secondary electron multiplier disposed in spatial relation to said field emission cathode such that electrons emitted from said cathode enter said multiplier in a direction which imparts a high-multiplying factor to said electrons; means for indirectly refrigerating said field emission cathode; and at least one accelerating electrode disposed in relation to said field emission cathode to guide an electron beam emitted from said cathode. 

1. A light detector comprising a field emission cathode of a photoconductive semiconductor; means for detecting variations in field emissions due to changes in light; a channel-type secondary electron multiplier disposed in spatial relation to said field emission cathode such that electrons emitted from said cathode enter said multiplier in a direction which imparts a highmultiplying factor to said electrons; means for indirectly refrigerating said field emission cathode; and at least one accelerating electrode disposed in relation to said field emission cathode to guide an electron beam emitted from said cathode. 